Add a new compressor interface; and the brotli compressor which is
similar to the existing bz2 one.
Also add a new CompressorType argument to PatchWriter's init function;
this allows us to choose the right compressor based on the input option
in the future.
Bug: 34220646
Test: Run bsdiff/bspatch with brotli compressor/decompressor over a
list of files from angler's system image. Make succeeds.
Change-Id: Id9a3db2d7d051dcb751a1fc362f4c3b9226e878b
